package com.wc.alorithm_luogu.P5708;

import java.util.Scanner;

/**
 * @Author congge
 * @Date 2023/4/17 18:32
 * @description https://www.luogu.com.cn/problem/P5708
 * 三角形面积
 */
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double a = scanner.nextDouble();
        double b = scanner.nextDouble();
        double c = scanner.nextDouble();

        double p = 0.5 * (a + b + c);

        double S = Math.pow(p * (p - a) * (p - b) * (p - c), 0.5);

        System.out.printf("%.1f", S);
    }
}
